Printers of this type, as well as such apparatus as magnetic drum memories or magnetic disk units, are used for recording data and include a magnetic recording carrier which takes various forms, such as a drum, an endless belt or a disk, and is coated with a film of magnetic material. The recording of the data on this carrier is accomplished by means of a recording device known as a transducer, which includes one or more magnetic recording heads in proximity with which the recording carrier is displaced. Each of these heads, each time it is excited by an electric current of suitable intensity, generates a magnetic field, with the effect that magnetized zones of small dimensions are created on the surface of the recording carrier that travels past these heads; these zones are practically in punctuate form and are generally known by the term magnetized points. The portion of the surfaces of the carrier that accordingly travels past each head is typically called the data recording track, and the recording carrier generally includes a plurality of tracks which can be subjected to the recording, either individually in the course of successive recording operations, or simultaneously in the course of a single operation. To obtain better definition of the magnetized zones or points formed on the recording carrier, it has been proposed that the carrier be magnetized using what is known as the transversal recording mode; that is, the magnetic induction of each zone, in each of the magnetized zones thus formed, is practically perpendicular to the surface of the carrier. One such magnetizing mode proved to be particularly interesting in the case of magnetic printers, where in order to obtain a high-resolution printed image, a magnetic latent image must be recorded on the carrier, the various constituent points of the image being very small and very close to one another. To record this magnetic image, the prior art has employed a transducer including a plurality of magnetic heads disposed beside one another and aligned in a direction perpendicular to the direction of displacement of the recording carrier, each of the heads including a thin magnetic core on which an excitation winding is wound. This core is substantially U-shaped and is profiled in such a manner that it has a relatively narrow recording pole at one of its ends and at its other end it has a relatively wide flux closing pole; these two poles are placed in contact with or in immediate proximity with the surface of the recording carrier.
These heads make it possible to obtain perfectly defined, relatively small magnetized points on the recording carrier, the points for instance having a cross section on the surface of the carrier on the order of 100 to 200 .mu.m on a side. However, they have the disadvantage that each includes a core, which in the course of manufacture must be machined with very great precision, if the magnetized points formed by these various heads are to be substantially identical in size. Furthermore, with these heads, the time required for forming a magnetized point on the recording carrier is always relatively long, typically exceeding 6 microseconds, which naturally limits the performance of the machine in which these heads are used. These heads also have the disadvantage that each includes a magnetic core having faces with a relatively large surface area, which are placed facing the faces of the adjacent cores, so that when an attempt is made to dispose these heads close to one another in order to increase the density of the magnetized points and thus improve the quality of the printed characters, the magnetic flux generated by the excited heads causes leakage of flux, which circulating in the cores of the heads adjacent to the excited heads then causes the formation of undesirable magnetized points on the surface of the recording carrier.
These disadvantages can be overcome by making use of recording heads having a magnetic core that is provided with an exciting coil and takes the form of a rod or needle; the cores of these heads each have one end located at least in the immediate proximity of the surface of the recording carrier, and these ends are aligned one with the other along a direction perpendicular to the direction of displacement of the recording carrier. With these heads, the core of which is easy to manufacture, the time required for recording a magnetized point does not exceed 2 microseconds. Nevertheless, the emplacement of these heads inside the same transducer has always been a difficult operation to perform, especially because of the small diameter of the cores and their low rigidity.
In an embodiment described and shown in U.S. Pat. No. 3,890,623, in which the filamentary cores have a diameter in the vicinity of 0.8 mm, this placement is obtained by initially piercing a first series of aligned holes in a first support plate, each of the holes having a diameter sufficient to allow the engagement with slight play of one of the two ends of a core, then inserting each core, provided with its winding, into each of these holes, then keeping the core in place on this first support plate by piercing a second series of holes in a second support plate, in such a manner that the second series of holes are located perpendicular to the holes of the first series, and finally causing the other end of each core to engage the corresponding hole of this second series.
This manner of assembly, which can be used in the case where the magnetic cores have a diameter at least equal to 0.5 mm, cannot be employed for a magnetic transducer having heads with magnetic cores that have a very small diameter, for example less than 0.1 mm. This is because the filamentary magnetic cores, having an equally small diameter, would have too little mechanical rigidity to undergo the various operations of assembly as described above without being deformed.